Do you have an OWC SSD? If you do there is a known issue with High Sierra with there SSD's running APFS. Review this: A Note on High Sierra Compatibility with Third Party SSD's
At this time I'm still waiting for Apple to fix a more generic issue with APFS running on SATA based SSD drives besides the special case with OWC's SSD's. The issue Apple has a queuing issue within the APFS and the Finder process so you'll encounter issues trying to save documents and URL's.
If you own an older Unibody MacBook Pro with an SATA based SSD you want to stick with Sierra for now.